Lap Time: 2:55.2

BMW’s F90 M5 is the quickest sedan we’ve ever run at Lightning Lap. But just barely. Its 0.2-second margin over the previous quickest, the Mercedes-AMG E63 S 4MATIC we ran here last year, makes the four-door contest a near wash. It’s not surprising that their armaments and tactics are similar. Both use twin-turbocharged DOHC V-8 engines making about 600 horsepower, transmissions smart enough to shift themselves better than we can, and all-wheel drive to put the power down.

The M5’s flexible engine plays a large part in making its quickness approachable. All 553 pound-feet of torque are available between 1800 and 5700 rpm, and the engine remains ardent all the way to its 7200-rpm redline. But the M5 is less aggressively tuned than the E63. Its larger V-8 lacks the E’s barking exhaust note. It doesn’t try to back into every corner like the AMG sedan does. We set our quickest time with the M5’s all-wheel-drive system in its standard setting rather than in Sport, which allows more yaw before activating the front axle.

Despite a better weight-to-power ratio (it’s about 300 pounds lighter than the E63), the M5 is 2.4 mph slower down the front straight than the AMG. But it almost completely erases its 0.5-second deficit in sector one by the bottom of the Climbing Esses, leaving it just 0.1 second behind the E63 after the track’s most speed-critical complex. The BMW regains that tenth before entering the downhill Spiral, making this limousine battle a dead heat with the most technical sections of the lap remaining. The M5 starts to edge the E63 climbing out of the infield, where it’s 0.3 second quicker before it gives up a tenth of a second through Hog Pen and past the start/finish to settle with a 0.2-second advantage.

Certainly these cars are aimed at the same buyer, and they’re pretty evenly matched on the road. But being this close on a racetrack reveals just how tight the supersedan arms race is.